[Vedrover]

Fellas, I have a silly question:
I'm doing a glass fuse to blade fuse conversion on a 1988 110, and, after looking at the diagram on the back side of the fuse box cover, I presumed that the fuse ratings there are shown for the surge (i.e., blowing) value. So I bought all the fuses approximately 1/2 of that (i., a 4 a spade fuse for a 8a glass fuse circuit).

Going through the replacement though, I noticed that all fuses actually match the continuous amperage rating of what's shown on the fuse box diagram (i.e., a 8A continuous/15A surge for a circuit shown as a 8A on a diagram).

Funny thing is that the 4A spade, installed in a 8A circuit doesn't blow (although that's on battery power, I haven't actually tried it with ignition on and engine running).

So, before I go through uprating the spade fuses to match continuous ratings, can anyone with older glass fuses (or someone who's done the fusebox conversion), please, confirm that their vehicle has the same setup and the previous owner didn`t just install incorrect fuses?

Here`s the fusebox diagram:

And here`s the fuses (high/low beams and markers)

Thanks!

 

[GynormousMellon]

Fellas, I have a silly question:
I'm doing a glass fuse to blade fuse conversion on a 1988 110, and, after looking at the diagram on the back side of the fuse box cover, I presumed that the fuse ratings there are shown for the surge (i.e., blowing) value. So I bought all the fuses approximately 1/2 of that (i., a 4 a spade fuse for a 8a glass fuse circuit).

Going through the replacement though, I noticed that all fuses actually match the continuous amperage rating of what's shown on the fuse box diagram (i.e., a 8A continuous/15A surge for a circuit shown as a 8A on a diagram).

Funny thing is that the 4A spade, installed in a 8A circuit doesn't blow (although that's on battery power, I haven't actually tried it with ignition on and engine running).

So, before I go through uprating the spade fuses to match continuous ratings, can anyone with older glass fuses (or someone who's done the fusebox conversion), please, confirm that their vehicle has the same setup and the previous owner didn`t just install incorrect fuses?

Here`s the fusebox diagram:

And here`s the fuses (high/low beams and markers)

Thanks!

Following. Just ordered the replacement parts to do my 89 110.

Sent from my Pixel XL using Tapatalk

 

[o2batsea]

You're going the wrong way on the math. Continuous is the nominal amp flow, and the blow rating is about double that for the British glass fuses. So for your AT type fuse you want the fuse to be TWICE the nominal rating, not half. If you look at the label on the fuse you'll see the blow rating listed under the nominal. AT fuses are rated at the blow amperes.
Fuses protect the WIRE, not the thing at the end of the wire. If you are putting more amps than the wire can withstand, it will (we hope) blow the fuse rather than melt the wire. Most automotive wiring is about 16 or 18 AWG or fatter. You can put about 30 odd amps thru wire that small no problem (it might get warm from resistance) so the fusing on these wires is a bit conservative for safety reasons.
Unless there is some huge compelling reason to switch the fuse panel, like you are completely rewiring the vehicle, You should just leave it as it is.

 

[Vedrover]

You're going the wrong way on the math. Continuous is the nominal amp flow, and the blow rating is about double that for the British glass fuses. Unless there is some huge compelling reason to switch the fuse panel, like you are completely rewiring the vehicle, You should just leave it as it is.

There's logic (perhaps, flawed) to my madness: when sizing new ATO fuses, I didn't look at the existing fuses, I looked at the diagram and presumed (probably, incorrectly) that it, in the British tradition, shows blow amps, not continuous amps. Then, since ATO fuses are rated for continuous current, I bought them approximately 1/2 of the diagram value.

Seeing during the dismantling that just about every fuse matches its continuous rating to the diagram values, I suspect that my original assumption was wrong and the diagram actually shows continuous amps, so I simply need my ATO fuses to match that value.

Before I conclude on that, I just want to make sure that there's at least one other vehicle in the same situation and the previous owner didn't just incorrectly replaced all the fuses (unlikely, but not unheard of).

As for the compelling reason for replacement, I have two: 1) hard to find smaller glass fuses plus when you find them they're expensive; 2) the fuse holders are old and loose, no fun losing power to lights etc., when I'm driving on crappy washboard pavement of Quebec.

------ Follow up post added February 23rd, 2018 06:23 AM ------

Following. Just ordered the replacement parts to do my 89 110.

Sent from my Pixel XL using Tapatalk

So, what do you have in your vehicle? Does your diagram match the continuous or blow amps of your fuses? If you still have British fuses, they will have dual rating (like 8/15A or clearly state it on the body like on the picture above). Otherwise it gets tricky, as some British fuses only show blow amps, and ALL American fuses only show continuous rating.

 

[o2batsea]

The ratings on the fuse panel are continuous, not blow. British glass fuses are always rated at the nominal amperage they carry, not the blow. The equivalent ATO fuse will be roughly double the number on the panel. Since it's difficult to find step ratings in single numbers, it's probably OK to round up to the next 5 amp increment. That is, the 2.5 would be 5A, the 8 be 15A, the 10 20A, the 12 25A, the 17 30A.

Britishwiring.com and autosparks.co.uk have the glass fuses and they are not expensive.

 

[Uncle Douglas]

When I replace a glass fuse box with blade type I stick with the same amp fuses and I use smart fuses because the fusebox location sucks. ATO Smart Glow Series - Indicator Fuses Automotive Aftermarket Products from Fuses - Littelfuse

Going higher amperage, ie lowering the safety factor isn't a place I'd go.

 

[Vedrover]

The equivalent ATO fuse will be roughly double the number on the panel.

Britishwiring.com and autosparks.co.uk have the glass fuses and they are not expensive.

Based on the specs and anything I've looked at for ATO fuses, they are rated for continuous (Amps they can carry under normal conditions), so, provided the diagram is for continuous as well, you shouldn't double-up the ATO rating, you should match it, so 8A/15A British = 7.5A ATO. Otherwise you have a 15A/30A ATO fuse where 8A/15A should be.

As for replacement fuses, sure, they are available online, but I just want to be able to get a spare in any village shop if I need to (still not easy for 7.5A fuses, of course, but easier than smaller glass ones for sure).

 

[Uncle Douglas]

fwiw- a good walk in source on the glass fuses is Tractor Suppy

 

[Vedrover]

British glass fuses are always rated at the nominal amperage they carry, not the blow. /QUOTE]

Sorry, but they are the opposite of that, they typically show either the dual hold/blow current or just the blow current. For example, look at my picture of the fusebox, there's a red fuse there that says just "5A" on it. That's a British 2.5A/5A fuse sitting in the marker lights circuit, marked as 2.5A on the diagram.

American fuses, on the other hand always show hold current. So a 5A fuse will typically hold 5A but blow at 10.

 

[GynormousMellon]

There's logic (perhaps, flawed) to my madness: when sizing new ATO fuses, I didn't look at the existing fuses, I looked at the diagram and presumed (probably, incorrectly) that it, in the British tradition, shows blow amps, not continuous amps. Then, since ATO fuses are rated for continuous current, I bought them approximately 1/2 of the diagram value.

Seeing during the dismantling that just about every fuse matches its continuous rating to the diagram values, I suspect that my original assumption was wrong and the diagram actually shows continuous amps, so I simply need my ATO fuses to match that value.

Before I conclude on that, I just want to make sure that there's at least one other vehicle in the same situation and the previous owner didn't just incorrectly replaced all the fuses (unlikely, but not unheard of).

As for the compelling reason for replacement, I have two: 1) hard to find smaller glass fuses plus when you find them they're expensive; 2) the fuse holders are old and loose, no fun losing power to lights etc., when I'm driving on crappy washboard pavement of Quebec.

------ Follow up post added February 23rd, 2018 06:23 AM ------



So, what do you have in your vehicle? Does your diagram match the continuous or blow amps of your fuses? If you still have British fuses, they will have dual rating (like 8/15A or clearly state it on the body like on the picture above). Otherwise it gets tricky, as some British fuses only show blow amps, and ALL American fuses only show continuous rating.

My fuses look pretty old and they are a mix of UK & US fuses. This should be interesting to straighten out.

 

[Red90]

American fuses, on the other hand always show hold current. So a 5A fuse will typically hold 5A but blow at 10.

That is not how fuses work. The number displayed is the continuous rating at 25 C that they are just on the edge of failing. What they will blow at is time, temperature and and amperage dependent. No fuses should ever be USED at their displayed value. What they are trying to tell you on the British fuses is you should not use them normally above 50% of their rating. This is just as true with the ATO fuses.

http://m.littelfuse.com/~/media/aut...cle/blade-fuses/littelfuse_atof_datasheet.pdf

 

[o2batsea]

“American” fuses show the current at which they pop.

------ Follow up post added February 23rd, 2018 04:21 PM ------

When I replace a glass fuse box with blade type I stick with the same amp fuses and I use smart fuses because the fusebox location sucks. ATO Smart Glow Series - Indicator Fuses Automotive Aftermarket Products from Fuses - Littelfuse

Going higher amperage, ie lowering the safety factor isn't a place I'd go.

This. However I can only find smart glow fuses in 5 amp increments.
Again, it’s protecting your wires, not the motors or lights

 

[Vedrover]

“American” fuses show the current at which they pop.

------ Follow up post added February 23rd, 2018 04:21 PM ------

Nope. HERE`s the link to, for example, Littelfuse`s spec sheet for their entire lineup of ATO SmartGlow blade fuses.

The only fuses that blow at 100% of the rating are their 35 and 40A fuses, and even then they only do so after 100 hours (mind you they made a mistake on the datasheet, putting "Opening Time" into the second column where "Current Rating" should be), without accounting for ambient temperature.
The rest blow after, at least 110%, and, to blow them at 1 second or faster, current must be at least at 135% of the rated amperage or more.

So, fuse science seems to have hijacked the conversation from the original topic of what the diagram shows: continuous or blow current?

I will be finishing the wiring today and for now I will assume that the existing fuses are sized correctly, and that the diagram shows continuous current rating.
Will err on the size of safety, going with 2A ATO for 2.5A British, 5A ATO for 5A British, 7.5A ATO for 8A British, 10A ATO for 10A and 12A British and 15A ATO for 17A British.

Was just checking the Workshop Manual: all the fuses in the manual (RTC4482 ~ RTC4510) state their blow current, so, for example, RTC4502, shown as 15A fuse in the manual is a 8A hold 15A blow fuse. So, they match the continuous current pattern, shown in the diagram, so, that's one more reason to believe the diagram shows continuous current values.

 

[o2batsea]

But we all learned something, so it's a win.

 

[Vedrover]

But we all learned something, so it's a win.

That`s why I love this forum: anyone walking into a conversation with a simple question walks out of it with a PHD in Roverology, and a 4-year apprenticeship in an adjacent field, from Mechanical to Structural to Electrical

 

[mdubs]

I recently bought replacement glass fuses and replacement relays when I was trouble shooting my blinkers. It is challenging to find these glass fuses in the weird amperage settings, but I got everything from https://www.brit-car.co.uk

Shipping was cheap too.

 

[Vedrover]

So, a quick update: rewiring all done, took approximately 2 hours start to finish. One of the 2A fuses that was used to replace the original 2.5A glass fuses didn't hold, so, up-rated both of them to 3A.

I've lost both the front and rear wipers, though. They both operated sluggishly at first and died completely after the first swipe (as if the motor(s) died, so that's not good). Only one of the fuses is blown (the 10A fuse that replaced the 12A glass fuse), the 5A for rear washer/wiper is fine. Both washer pumps remained operational too. Everything else works fine.
So, I will be investigating this now.....

 

[Vedrover]

So I got the wipers to work too. But I don't like that the windshield wiper motor is getting pretty warm pretty fast. I'll re-crimp the wires for these particular terminals (just in case I maybe accidentally cut off some strands when stripping the insulation). Or maybe the motor is just on its last breath and about to pack it because of age.

 

[GynormousMellon]

So I got the wipers to work too. But I don't like that the windshield wiper motor is getting pretty warm pretty fast. I'll re-crimp the wires for these particular terminals (just in case I maybe accidentally cut off some strands when stripping the insulation). Or maybe the motor is just on its last breath and about to pack it because of age.

You have my undivided attention now!

Sent from my Pixel XL using Tapatalk

 

[Vedrover]

New working setup

Here's my working setup for spade fuses (it, basically, matches the original setup, but is corrected for standard available ATO fuse amperages):